Pressure tank



April 25, 1944. W TEETER 2,347,379

PRESSURE TANK Filed NOV. 30, 1942 AUNITED sTATEs PATENT orrxcs PRESSURE TANK Wilford Teeter, Dayton, Ohio, assigner to General Motors Corporation, Dayton, Ohio, a corporation of Delaware Application November 3o, '1942, serial No. 467,439

7 Claims.

This invention relates to pressuretanks and more particularly to pressure tanks for hydraulic pressure systems now widely used in large airplanes, but which are capable ofvuse in practically any pressure system.`

Hydraulic systems e'inploying pressure tanks are commonly used for many things including the actuation of airplane control devices and landing gears. The requirements of such a system for airplanes are unusually vsevere because of the great range of temperature to which it may possibly be subjected, as well as the greatly desired light weight requiring the use of high pressures. Because the pressure tank in an airplane is subjected to violent movement and agitation in different directions and/or because the high pressures involved would cause the air to dissolve in the liquid and/or because the liquid used may be inflammable, it is necessary to use a flexible Wall for separating the air from the liquid in the pressure tank: Under such conditions there has been a high rate of failure of the exible walls.

believe that the principal reason for the failure of the flexible walls is that they are overstressed when the exible walls are deected to increase the amount of the hydraulic uid in the pressure tank. The pressure tanks or accumulators are spherical in shape and commonly contain as the separating iiexible wall a bladder like a basket ball, although some prefer a hemispherical flexible Wall. The hydraulic uid is pumped into the space between the bladder and the outer wall. When the tank is empty the bladder is pressed tightly against the tank wall (Cl. 13S-.30)

flexible wall from being pressed tightly against the tank wall without any equalizing force.

It is another object of my invention to provide an improved method of operating and equalizing the forces within a pressure tank or accumulator of hydraulic systems.

Generally speaking, these objects are attained by providing some means such as a perforated inner spacing wall whereby the hydraulic fluid is always present between the bladder and the tank wall, preferably over an area of substantially half the area of the inside of the tank, or at least a substantial portion thereof. Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred form of the present invention is clearly shown.

In the drawing the figure shows a sectional view through an accumulator or pressure tank together with a diagrammatic representation of other portions of a hydraulic system for airplanes.

Referring now to the drawing, there is shown diagrammatically, for the purpose of illustrating one of the most important applications of the invention, a hydraulic system for an airplane in cluding a gear pump 20, normally driven by one of the engines of an airplane. 'I'his pump 20 pumps a suitable hydraulic uid, such as oil, from the lowvpressure side of the system to the high pressure side of the system. A by-pass 22 connects the discharge side of the pump 20 with the intake side and is provided with a pressure by the air pressure within the bladder without relief valve 24 Which Will Open the by-DaSS at any balancing force. `To deflect the bladder to some suitable pressure such as 1000 lbs. or 1500 accommodate more hydraulic fluid there must be lbs., per square inch. suicient excess of the hydraulic liquid pressure The pump 20 discharges into a high pressure over the air -pressure upon the area separated supply line 26, one branch of which is provided from the tank wall by the hydraulic liquid, to with a three-way valve 28 which connects the inpull the bladder away from the wall against which terior of the brake cylinders 30 with either the it is pressed. 'Ihis overstresses the bladder or high pressure supply line or the discharge line flexible wall, stretches it and causes early fail- 32 connecting with the intake side of the pump ure. It also may cause some unevenness in pres- 20. To apply the brakes of the airplane the valve sure and delivery within the hydraulic system. 45 28 is turned so that the high pressure line 26 is It is an object of my invention to provide connected to the brake cylinders 33 to press the means for preventing overstressing and failure brake shoes against the brake drums upon the of the flexible wall in pressure tanks or aclanding Wheels. When the brakes are to be recumulators. leased, the valve 28 is turned so that the interior It is another object of my invention to proof the cylinders are connected to the discharge vide means for preventing unevenness in the line 32. Y pressure and delivery within a hydraulic system A fOllr-Way valve 34 controls the connection of having a pressure tank or accumulator. the wing flap cylinder 36 With thehigh pressure It is another object of my invention to provide line 26 and the branch 38 which connects to the a means for preventing the movable part of the discharge line 32. With this four-way valve either end of the piston may be connected to the high pressure line while the alternate end will then be connected to the discharge line. This controls the position of the wing naps.

A four-way valve 48 connects the landing gear cylinders'42 with the supply and discharge lines. When it is desired to lower the landing gear, the four-way valve 48 is turned so that the upper ends of the cylinders` are connected to the high pressure line and the lower ends of the cylinders are connected to the discharge line. When it is desired to raise the landing gear, the four-way valve 40 is turned 180 so that the lower end of the cylinders are connected with the high pressure line and the upper ends of the cylinders with the discharge line.

Inasmuch as the capacity of the pump 20 is comparatively small and it is desired that the pistons in these various'operating cylinders move rapidly it has been customary to provide a pressure tank or accumulator for providing a reserve supply of hydraulic fluid under pressure. To accommodate this accumulator, a line 44 connects to the discharge line 26 at one end and connects to the tting 45 providing an inlet port at the top of the pressure tank or accumulator 46 at the other end. This accumulator includes an outer spherical shaped wall to withstand internal pressure. This wall I preferably form from a lower hemispherical metal wall 48 and an upper hemispherical metal wall 58 which are joined together by a lap joint 52 which may be welded by any suitable means.

There is a large aperture provided in the bottom of the lower wall 48 and the edges of this aperture are clamped between the collar 54 and the nut 56. Within the walls of the tank there is provided a flexible diaphragm or bladder 58 which is made of a synthetic rubber-like material and has its lower end shaped so as to provide a bead 60 which is held between the rim of the collar 54 and the valve member 62 by the gland nut 66. The interior of the bladder 58 is filled with air to a suitable pressure, such as 250 lbs. per square inch, through the standard check valve 68, which is normally provided in the valve member 62. The lower half of the bladder is provided with a heavier wall than the upper half and particularly is provided with an annular shoulder 64 which ilts the shoulder formed by the lap joints between the upper and lower walls 58 and 48. This is done so that there will be a tendency for the upper portion of the bladder to be deflected rather than the lower portion which will normally be prevented from shifting by the shoulder 64.

There has been great dilliculty preventing failure of these bladders or flexible walls. The high pressure within the bladder causes the bladder to be pressed tightly against the inside of the tank or accumulator wall composed of the members 48 and 50. The hydraulic iluld enters the accumulator through the fitting 45 and has suilicient pressure to forcibly deflect the bladder downwardly adjacent the fitting 45. This provides a small volume 1l containing the hydraulic fluid. Under static conditions, that is, when no fluid is entering or leaving, the pressure on the opposite sides of the diaphragm adjacent this space 10, are equal. When, however, the pressure upon the discharge side of the pump 20 rises, there will be a rise in the pressure ln the space 10. This rise in pressure will be opposed by the pressure within the bladder. It, however, will .also be opposedby the pressure'at the points 12 and 14 at which points the full pressure of the Y air is exerted to hold the bladder tightly against the inside wall of the tank or accumulator. The pressure at this point in the ordinary accumulator is unbalanced and tends to seal the bladder to the walls of the tank. The pressure within the space acting upon the portion of the diaphragm separated from the wall of the tank must become in excess of the pressure within the bladder before the bladder can be separated and pulled away from the tank wall to overcome the pressure at the points 12 and 14, which tends to hold the bladder tightly against the wall of the tank. I believe that this causes excessive stretching and overstressing of the diaphragm between the points 12 and 14 causing early failure of the diaphragm.

In order to overcome these serious objections, I have provided a method and a means whereby' the hydraulic fluid will always be present between the wall of the tank and the upper or movable half of the bladder. To do this, I have provided a perforated inner wall or spacing member 16 of hemispherical shape which is held in place by the flange provided by the lap joint, 52. The lower edge of this spacing wall 16 is turned outwardly and the wall 58 is provided with indentations 18 for holding the perforated spacing wall 16 away from the tank wall so that the hydraulic fluid can pass around the spacing member 16 and through the apertures in the spacing wall 16 into contact with all the portions of the upper half of the bladder.

By this arrangement, instead of the upper hall of the bladder being pressed tightly against the wall of the tank, it is pressed against the spacing wall 16. But this pressure is opposed by the hydraulic pressure which acts upon the outside oi the bladder through the perforations in the spacing wall 16. When there is an increase in pressure upon the discharge side of the pump 20 and an increase in the volume, the space 10 is increased in size and only a slight excess in pressure in the space 18 over the air pressure within the bladder 58 is required to forcibly deflect the bladder downwardly to increase the amount of hydraulic fluid within the accumulator. With this arrangement the tendency of the bladder to stick to the wall of the tank is prevented in the upper or movable half of the bladder. By this arrangement the excessive stretching of the bladder is avoided and the life of the bladder is greatly increased.

While I have illustrated my invention as applied to a hydraulic system for airplanes, it is applicable to all pressure ,systems wherein a pressure tank is desirable.

While the form of embodiment of the invention as herein disclosed, constitutes a preferred form it is to be understood that others forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

l. In a hydraulic pressure system, a pressure tank provided with a wall capable of withstanding internal pressure, an elastic wall dividing the interior of the tank into a primary chamber' and a secondary chamber, the primary chamber containing uid under pressure, the wall oi` thc tank being provided with a port connecting the secondary chamber with the hydraulic system, and means for preventing the sealing off of remote portions ofthe secondary chamber from access to said port by said velastic wall when said :secondary chamber is greatly reduced in size.

2. In a hydraulic pressure system, a pressure tank provided with a wall capable of withstanding internal pressure, an elastic wall dividing the interior of the tank into a primary chamber and a secondary chamber, the primary chamber 5 containing uid under pressure, the wall of the tank being provided with a port connecting the secondary chamber with the hydraulic system, the interior wall of said tank being provided with passages connecting said port with some parts 1o of the secondary chamber remote from said port.

3. In a hydraulic pressure system, a pressure tank provided with a wall capable of withstanding internal pressure, an elastic wall dividing the interior of the tank into a primary chamber 15 and a secondary chamber, the primary chamber containing fluid under pressure, the wall of the tank being provided with a'port connecting the secondary chamber with the hydraulic system,

the interior wall of said tank being provided with 20 and a secondary chamber, the primary chamber 3 containing uid under pressure, the wall of the tank being provided with a port connecting the secondary chamber with the hydraulic system, one of said walls being provided with a construction for preserving communication between said y,.-

port and some parts of the secondary chamber remote from said port when said secondary chamber is greatly reduced in size.

5. In a. hydraulic pressure system, a pressure tank provided with a wall capable of withstand- 40 ing internal pressure, an elastic wall dividing the interior of the tank into a primary chamber and a secondary chamber, the primary chamber containing fluid under pressure, the wall of the tank being provided with a port connecting the secondary chamber with the hydraulic system, one of said walls being provided with passageforming means providing 4communication between said port and some parts of the secondary chamber remote from said port when said elastic wall is substantially in contact with some of the wall portions of said tank.

6. In a hydraulic pressure system, apressure tank provided with a wall capable of withstanding internal pressure, an elastic wall dividing the interior of the tank into a primary chamber and a secondary chamber, the primary chamber containing uid under pressure, the wall of the tank being provided with a port connecting the secondary chamber with the hydraulic system, an inner wall located adjacent said port between said elastic wall and the wall of said tank and spaced from the wall of the tank in some areas for providing free passage of fluid into and out l of said port.

'7. In a hydraulic pressure system, a pressure tank provided with a Wall capable of withstanding internal pressure, an elastic wall dividing the interior of the tank into a primary chamber and a secondary chamber, the primary chamber containing uid under pressure, the wall of the tank being provided with a port connecting the secondary chamber with the hydraulic system, an inner wall located adjacent said port between said elastic wall and the wall of said tank and spaced from the wall of the tank in some areas for providing free passage of fluid into and out of said port, said inner wall being perforated and covering nearly half the wall of the tank.

WILFORD H. TEETER. 

